This invention relates generally to the art of remote angle measurement, especially to devices such as those used for measuring the pitch angle of a model plane in a wind tunnel. More specifically, the invention concerns holographic angle measurement devices.
The present invention was developed to accurately measure pitch angle of a model plane in a wind tunnel, although the invention is useful in other angle measurement applications as well. Generally, prior art devices for measuring pitch angle in wind tunnels have utilized indirect measurement techniques. For instance, one device uses a pendulum and accelerometer arrangement to measure the change in vertical angle of the model. From this measurement, the pitch angle of the model is then calculated.
In another device, the angle of the supporting rod for the model, which is called the sting, is measured with a geared potentiometer. The forces on the model which produce sting deflection are measured with a load cell. From these measurements, the pitch angle of the model is calculated.
In still another device, which is useful in wind tunnel arrangements in which models are mounted on pedestals which extend upward from the floor of the wind tunnel, a potentiometer is connected to the arm of the pedestal in such a manner that a change in angle of the arm results in a change in measured resistance of the potentiometer. The pitch angle is then calculated from the measured resistance.
In the past, the results produced by such devices have been sufficiently accurate to warrant their use. However, with increasing emphasis on maximum aircraft efficiency, requiring sophisticated design techniques and testing devices, greater accuracy than that provided by such prior art devices is now necessary.
Besides low accuracy, however, these devices have another significant disadvantage, in that their results are not dynamic, i.e. there is often considerable delay between initial data measurement and the actual results, since both the basic measurement and calculation steps require considerable time. In many cases, the angle being measured has changed substantially by the time the angle information is obtained from the device. Hence, the information is often out-of-date by the time it is obtained, and sometimes no longer useful.
It is a general object of the present invention to provide an angle measurement system which overcomes one or more of the disadvantages of the prior art discussed above.
It is another object of the present invention to provide a single angle measurement device which is capable of measuring the pitch, roll and/or yaw angles of a model in a wind tunnel.
It is a further object of the present invention to provide such an angle measurement device which is more accurate than those of the prior art.
It is yet another object of the present invention to provide such an angle measurement device which provides results in real time.